This invention relates generally to crystalline olefin polymers and production thereof and more particularly to a new and advanced process for producing crystalline olefin polymers.
The term "polymer" as used in this specification, including the claims, is intended to include homopolymers and copolymers unless otherwise specified.
It is well known that crystalline polyolefins can be obtained, in general, by polymerizing olefins in the presence of catalytic systems comprising organometallic compounds of metals of group 1, 2, and 3 of Mendelejeff's periodic table and halogen compounds of transition metals of group 4, 5, and 6 of the periodic table in the presence of an inert solvent.
It is also known that, in order to produce the crystalline polyolefins in high yields in such cases, combinations of organoaluminum compounds as the organometallic compounds and titanium compounds of lower valence than the maximum valence, e.g., titanium trichloride, as the halogen compounds of transition metals are being used in an industrially advantageous manner.
However, according to the results of our experiments, for example, when a catalytic system comprising triethyl aluminum and titanium trichloride is used in the homopolymerization of propylene, the quantity of matter insoluble in boiling heptane, i.e., the crystalline polymer, is from 70 to 85 percent of the total polymer formed. Furthermore, when a catalytic system comprising diethylaluminium chloride and titanium trichloride is used, the quantity of the above mentioned boiling heptane insoluble matter is from 85 to 90 percent, this proportion of the boiling heptane insoluble matter being known as the isotactic index (II).
Thus, even when a catalytic system of a combination which, among Ziegler type catalysts, is thought to form a relatively small proportion of boiling heptane soluble matter is selected, the proportion of the boiling heptane soluble matter relative to the total polymer formed is still from 5 to 30 percent.
In the production of a copolymer of two or more monomers, for example, in the case where propylene and ethylene are caused to undergo copolymerization, an increase in the ethylene content gives rise to an abrupt increase in the by-product quantity of non-crystalline copolymer, whereby there is a marked decrease in the yield of the crystalline polymer.
According to the results of our experiments, in the case where the ethylene content within an ethylene/propylene copolymer obtained is 2 percent, the quantity of the boiling heptane insoluble matter is from 40 to 60 percent of that of the total polymer formed when a catalytic system comprising triethyl aluminum and titanium trichloride is used. Furthermore, when a catalytic system comprising diethyl aluminum chloride and titanium trichloride is used, the quantity of the above mentioned boiling heptane insoluble matter is from 55 to 75 percent.
A polymer which dissolves in boiling heptane is ordinarily non-crystalline and, at present, is not known to have any suitable use. Furthermore, the formation as a by-product of this unnecessary non-crystalline polymer during the production of a crystalline polymer gives rise not only to an unnecessary consumption of the monomer but also to the necessity of extracting and removing the non-crystalline polymer from the polymer formed. Consequently, great industrial disadvantages such as complication of process and the necessity of increasing the equipment capacity or the number of machines are incurred.
Moreover, in cases where the proportion of matter soluble in boiling heptane becomes greater than 50 percent relative to the total polymer formed, various difficulties are encountered, although differing with the production process. In the ordinary process for producing polyolefins, difficulties such as an increase in the viscosity of the polymer slurry give rise to defective operation such as difficulty of removal of heat from the polymerization apparatus, clogging of piping, and lowering of operational capacity, whereby practical production on a commercial basis becomes impossible.
Accordingly, the discovery of a catalytic system, the use of which results in the formation of a small proportion of the non-crystalline polymer, would be of great industrial value. However, even if it causes the production of a small proportion of the non-crystalline polymer, a catalytic system cannot be utilised in an industrially advantageous manner if it gives rise to deleterious effects such as a remarkably adverse effect on the molecular weight of the polymer obtained, a drop in the polymerization velocity, or a lowering of the bulk density of the solid polymer obtained.